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Goodwill and Other Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Millions | 2 Months Ended | 3 Months Ended | 5 Months Ended | 9 Months Ended
--- | --- | --- | --- | ---
Jun. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2017
Goodwill [Roll Forward] |  |  |  |  |  |
Goodwill, beginning balance |  |  |  |  | $ 25.9 |
Unallocated acquisition date fair value of intangible assets, beginning balance |  | $ 436.2 |  |  |  |
Intangible assets, gross (including goodwill), beginning balance |  |  |  |  | 96.9 |
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | (436.2) |  |  |  |
Amortization |  | 7.4 | $ 2.4 |  | 12.9 | $ 7.3
Goodwill, ending balance |  | 321.4 |  | $ 321.4 | 321.4 |
Intangible assets, net (including goodwill), ending balance |  | 485.2 |  | 485.2 | 485.2 |
Unallocated acquisition date fair value of intangible assets, ending balance | $ 436.2 | 0.0 |  | 0.0 | 0.0 |
Intangible assets, gross (including goodwill), ending balanc |  | 532.9 |  | 532.9 | 532.9 |
Other Intangible Assets |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Intangible assets, net (excluding goodwill), beginning balance |  | 30.7 | 14.4 |  | 36.2 | 19.3
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | 140.9 |  |  | 140.9 |
Foreign currency translation |  | (0.4) |  |  | (0.4) |
Amortization |  | (7.4) | (2.5) |  | (12.9) | (7.4)
Intangible assets, net (excluding goodwill), ending balance | 30.7 | 163.8 | 11.9 | 163.8 | 163.8 | 11.9
Intangible Asset and Goodwill |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Intangible assets, gross (including goodwill), beginning balance |  | 492.8 | 40.3 |  | 62.1 | 45.2
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  |  |  |  | 436.2 |
Foreign currency translation |  | (1.6) |  |  | (1.6) |
Adjustments to reflect acquisition date fair value |  | 1.4 |  |  | 1.4 |
Amortization |  | (7.4) | (2.5) |  | (12.9) | (7.4)
Intangible assets, gross (including goodwill), ending balanc | 492.8 | 485.2 | 37.8 | 485.2 | 485.2 | 37.8
Goodwill |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Goodwill, beginning balance |  | 25.9 | 25.9 |  | 25.9 | 25.9
Attribution of acquisition date fair value estimates between goodwill and other intangible assets |  | 295.3 |  |  | 295.3 |
Foreign currency translation |  | (1.2) |  |  | (1.2) |
Adjustments to reflect acquisition date fair value |  | 1.4 |  |  | 1.4 |
Goodwill, ending balance | 25.9 | 321.4 | $ 25.9 | 321.4 | 321.4 | $ 25.9
NSM Holding Co LLC |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Intangible assets, net (including goodwill), ending balance |  | 431.0 |  | 431.0 | $ 431.0 |
NSM Holding Co LLC | Other Intangible Assets |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Foreign currency translation |  |  |  | 0.4 |  |
Amortization | $ 1.8 | $ 3.2 |  |  |  |
NSM Holding Co LLC | Goodwill |  |  |  |  |  |
Goodwill [Roll Forward] |  |  |  |  |  |
Foreign currency translation |  |  |  | $ 1.2 |  |

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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266 + Details
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- Definition Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e961-128460 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267 + Details
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- Definition Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance. + References No definition available. + Details
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